<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    手机号: <input type="number"> <button>发送</button>
    <script>
        var btn = document.querySelector('button');
        var time = 3;
        btn.addEventListener('click',function(){
            btn.disabled = true;
            
            let timer = setInterval(function(){
               if(time==0){
                clearInterval(timer);
                btn.innerHTML = "发送";
                btn.disabled = false;
                time = 3;
            }else {
                btn.innerHTML = "还有"+time+"秒";
                time--;
            }
            },1000);
            
        })
    </script>

</body>
</html>